The present invention relates to an apparatus and method for the preferably continuous manufacture of foamed material, such as foamed glass or ceramic material, using a furnace.
Foamed glass and ceramic materials are used in the form of blocks, bricks, sheets and the like having various cross-sectional shapes, including triangular, cylindrical and ovoid. Such material can be used for a great variety of products due to its low density, its abrasivity, its excellent thermal insulating characteristics, and its comparative high strength. The foamed material is generally produced by combining a mixture of glass or ceramic powder and a suitable foaming agent in a mold; the mixture is heated so that it first sinters, then fuses, and then foams, whereby the mixture expands to provide pores or bubbles therein.
In general, the mixture of glass or ceramic powder and foaming agent is heated to about 1250.degree. F. so that the material will sinter or coalesce. The material is then heated to from 1274-1700.degree. F. or higher to form a foamed block that is in a plastic state. This foamed material is then cooled to about 1050.degree. F. to rigidify the surface. The foamed material must be removed from the mold at this time. If not, and if the foamed material is cooled further, the thermal contraction of the mold will exceed the thermal contraction of the foamed material and the mold will "lock on" to the foamed material, especially if it is cooled to mold removal temperatures of from 100-150.degree. F. This can lead to crushing or rupturing of the cooled foamed material, and can make mold removal extremely difficult if not impossible.
Pursuant to heretofore known procedures, all commercially produced foamed glass or ceramic is foamed in discrete molds of various shapes and sizes. The foamed material, which is in the form of blocks or blanks, must be removed from the individual molds at a high temperature, whereupon the molds and lids therefor must be cleaned, refilled, and reinserted into a furnace. The foamed material must then be annealed, cooled, and cut into a finished product configuration from the larger blanks.
In view of the above, it can be seen that it would be advantageous to be able to produce foamed material in a continuous process in order to produce a more economical product. Several attempts have in the past been made to provide such a continuous process. For example, U.S. Pat. Nos. 3,585,014 and 3,607,170, to Malesak, and U.S. Pat. Nos. 4,038,063 and 4,124,365, to Williams, disclose the use of a thin, flexible belt on which to foam material as it travels through a furnace. Such a thin belt does not last long in a hot furnace environment, and it tends to warp, abrade and quickly deteriorate. Lubrication of the belt to restrict wear frequently fails in the hot furnace. In addition, the foamed material frequently sticks to the belt and builds up on the belt, even if release coatings are provided, due to the difficulty of cleaning and recoating the belt with release agent inside the furnace at high temperatures. U.S. Pat. No. 4,289,521, to Schymura, utilizes an overhead trolley to convey continuous molds through a custom built tunnel furnace. The molds are complicated, and rely on hinged sides. Failure of the hinge mechanism in a hot furnace environment would make it necessary to shut down the entire furnace and trolley system in order to remove and replace a failed mold and to clean up spilled foamed material. In addition, the sand seal that is used in the overhead trolley system requires constant replenishment of the sand in order to maintain the heat seal. Other continuous foamed glass systems use molds that are pushed end-to-end through the furnace. The pushing force required to overcome friction in a long furnace can deform the molds, resulting in an irregular continuous strip that would have to undergo additional trimming before it could be used. U.S. Pat. Nos. 3,972,667, Hanusa, 3,574,583, Goldsmith, 3,532,480, D-Eustachio, and 3,056,184, Blaha, utilize some type of roller mechanism in order to align and/or compress the foamed material. The rollers must be constantly coated with a release material in order to prevent build-up of the sticky foamed material, which could deform the continuous product. The use of rollers precludes the production of shapes that do not have flat or parallel surfaces. In addition to the aforementioned drawbacks of prior known processes, these processes also require the use of custom built furnaces, thus greatly adding to the cost of these known processes.
Thus, it is an object of the present invention to not only provide a potentially continuous process for the production of foamed material while avoiding the drawbacks of the heretofore known processes, it is also an object of the present invention to be able to produce finished material having any desired shape, whereby it is merely necessary to cut the finished product to a desired length. A further object of the present invention is to make it possible to change the shapes of the mold being used without having to shut down the apparatus and furnace while making such changes. It is yet another object of the present invention to be able to use a standard furnace.